Many synthetic resins which may be formed by emulsion polymerization are well known in the art. It is not difficult to form stable aqueous dispersions of such resins by addition of the resin feed an appropriate dispersing agent and catalyst to water with stirring. However, emulsification of resins produced by other polymerization techniques require that the bulk polymer must be dispersed in water to obtain an aqueous dispersion. Such a type is the hydrocarbon resins produced from steam-cracked petroleum fractions.
These hydrocarbon resins, i.e. petroleum resins, are defined herein as the thermoplastic resins obtained by polymerization, in the presence of a catalyst of the Friedel-Crafts type, of steam cracked petroleum distillates, boiling in the range between about 30.degree. and 280.degree. C., or any fraction of these distillates boiling within the said range, or of mixtures of olefins and diolefins containing sufficient diolefins to obtain a resin and not an oil or a rubbery material. This polymerization is performed at temperatures which range generally from 0.degree. to 70.degree. C., and for preference from 30.degree. C. to 55.degree. C.
These resins are polydienic in character and generally have a ring and ball softening point between about 0.degree. C. and 180.degree. C.
Since these resins are solid at room temperature numerous approaches have been utilized to produce aqueous emulsions of said resins for application as an adhesive, as a saturant or coating for paper or cloth or as a sizing or binding material in paper pulp.
One approach was to solvate the resin in hydrocarbon solvent and then combine resin solution and water. Invariably some residual hydrocarbon solvent remains in the finished emulsion, and this is undesirable in certain applications. This has led to the development of solvent-free dispersions (see U.S. Pat. No. 2,809,948) and emulsions (see U.S. Pat. No. 3,377,298) of petroleum resins. In both of these formulations, ionic emulsifiers have been utilized; in the former a mixture of cationic and non-ionic surface active agents is used to achieve a resin dispersion; and, in the latter an ionic surfactant is used in combination with an aqueous gel of a swelling earth to produce an emulsion paste of a petroleum resin.
Petroleum resin emulsions containing a large portion (10 to 70%) of diluents such as linseed oil and waxes and paraffins are taught in French Pat. No. 1,452,875 and German Offen. No. 2014652 respectively. However, such large percentages of diluent can materially modify, not always favorably, the properties of the base resin.
The emulsion pressure sensitive adhesives desirably should be derived in part from aqueous emulsions of tackifying resins, i.e. that resin which enhances the adhesive properties of a polymer system used as the adhesive. The tackifying resins include the herein defined petroleum resins. For a general discussion of the foregoing (including its commercial aspects) see the published talk entitled Resin Dispersions for Water Based Pressure Sensitive Adhesives by Robert W. Wherry and presented at The Pressure Sensitive Tape Council Seminar on Water Based PSA Systems in June of 1979.
The invention has for one of its objects the provision of aqueous dispersions of hydrocarbon resins of high shelf and mechanical stability.
A further object is to provide petroleum resins in the form of a latex-like dispersion for application as a pressure sensitive adhesive, as a saturant or coating for paper or cloth, or as a sizing or binding material in paper pulp.